DTRSV(l) BLAS routine DTRSV(l)
NAME
DTRSV - solve one of the systems of equations A*x = b, or A'*x = b,
SYNOPSIS
SUBROUTINE DTRSV ( UPLO, TRANS, DIAG, N, A, LDA, X, INCX )
INTEGER INCX, LDA, N
CHARACTER*1 DIAG, TRANS, UPLO
DOUBLE PRECISION A( LDA, * ), X( * )
PURPOSE
DTRSV solves one of the systems of equations
where b and x are n element vectors and A is an n by n unit, or non-unit, upper or lower
triangular matrix.
No test for singularity or near-singularity is included in this routine. Such tests must
be performed before calling this routine.
PARAMETERS
UPLO - CHARACTER*1.
On entry, UPLO specifies whether the matrix is an upper or lower triangular matrix
as follows:
UPLO = 'U' or 'u' A is an upper triangular matrix.
UPLO = 'L' or 'l' A is a lower triangular matrix.
Unchanged on exit.
TRANS - CHARACTER*1.
On entry, TRANS specifies the equations to be solved as follows:
TRANS = 'N' or 'n' A*x = b.
TRANS = 'T' or 't' A'*x = b.
TRANS = 'C' or 'c' A'*x = b.
Unchanged on exit.
DIAG - CHARACTER*1.
On entry, DIAG specifies whether or not A is unit triangular as follows:
DIAG = 'U' or 'u' A is assumed to be unit triangular.
DIAG = 'N' or 'n' A is not assumed to be unit triangular.
Unchanged on exit.
N - INTEGER.
On entry, N specifies the order of the matrix A. N must be at least zero.
Unchanged on exit.
A - DOUBLE PRECISION array of DIMENSION ( LDA, n ).
Before entry with UPLO = 'U' or 'u', the leading n by n upper triangular part of
the array A must contain the upper triangular matrix and the strictly lower trian-
gular part of A is not referenced. Before entry with UPLO = 'L' or 'l', the lead-
ing n by n lower triangular part of the array A must contain the lower triangular
matrix and the strictly upper triangular part of A is not referenced. Note that
when DIAG = 'U' or 'u', the diagonal elements of A are not referenced either, but
are assumed to be unity. Unchanged on exit.
LDA - INTEGER.
On entry, LDA specifies the first dimension of A as declared in the calling (sub)
program. LDA must be at least max( 1, n ). Unchanged on exit.
X - DOUBLE PRECISION array of dimension at least
( 1 + ( n - 1 )*abs( INCX ) ). Before entry, the incremented array X must contain
the n element right-hand side vector b. On exit, X is overwritten with the solution
vector x.
INCX - INTEGER.
On entry, INCX specifies the increment for the elements of X. INCX must not be
zero. Unchanged on exit.
Level 2 Blas routine.
-- Written on 22-October-1986. Jack Dongarra, Argonne National Lab. Jeremy Du
Croz, Nag Central Office. Sven Hammarling, Nag Central Office. Richard Hanson,
Sandia National Labs.
BLAS routine 16 October 1992 DTRSV(l)